Energy Transfers and Nutrient Cycles Flashcards
(28 cards)
Biomass
mass of carbon or dry mass of tissue per unit area
Suggest how to determine the chemical energy store in dry biomass
- calorimetry
- burn in pure oxygen and heat water until no further change in mass
Suggest limitations of biomass measurements
- accurate measurement involves removes all water from an organism which kills it
- estimations based on samples can be unrepresentative
Give reasons why only 1% of light energy is captured by plants
- reflected by water vapour and particulates in atmosphere
- wrong wavelength of light so not absorbed
- light misses chloroplasts
Gross Primary Production
- chemical energy stored in plant biomass in a given AREA
- production = kJm^-2 and productivity kJm^-2year^-1
Suggest how sugars and other organic compounds synthesised by plants are used
- respiratory substrates
- stored as biomass
Net Primary Production
- chemical energy stored in plant biomass for a given AREA after respiratory losses to the environment have been taken
into account - NPP = GPP - R
Suggest what net primary production is available for
- plant growth
- plant reproduction
- available to consumers at other trophic levels
Net Primary Production of consumers
N = I - (F + R)
where I = chemical energy store in ingested food, F
= chemical energy lost to the environment in faeces and
urine and R = respiratory losses to the environment
Explain why most food chains only reach four or five trophic levels at most
- energy lost at each stage of food chain
- insufficient energy to support a large enough breeding population
How to increase GPP and NPP of plants
GPP
- high light intensity via open field/artificial light of correct wavelength
- warm temperature via warm climate/heaters
- plentiful water supply via rainfall/irrigation
- rich mineral supply via fertilisers
NPP
- selectively bred
Describe how and explain why the efficiency of energy transfer is different at different stages in the transfer
- some light energy fails to strike chloroplast/is reflected/not of appropriate wavelength
- efficiency of photosynthesis in plants is low/approximately 2% efficient
- respiratory loss / excretion / faeces / not eaten
- loss as heat
- efficiency of transfer to consumers greater than transfer to producers/approximately 10%
- efficiency lower in older animals/herbivores/ primary consumers/warm blooded animals
- carnivores use more of their food than herbivores
Explain briefly how to improve efficiency of energy transfer in human food chains
- simplify food webs by removing competitors and pests
- reduce respiratory losses
- keep food chains short
Intensive Farming
- optimal conditions
- reduce respiratory losses
- high efficiency of energy transfer hence net production
- maximise profits
Explain how intensive rearing of livestock increases net productivity
- keep in enclosed spaces to limit movement/warm so more energy for growth
- controlled diet with high nutrient concentration
- protect from predators
- selectively breed
- slaughter before fully grown
Evaluate the use of chemical pesticides in intensive farming
- kills pests directly
- immediate response
- pest can develop resistance
- expensive/frequent treatment
- pollute water sources
Evaluate the use of biological agents
- little environmental impact in terms of pollution
- cheaper since predator species reproduces
- gradual process
- could become pests themselves
- could leave area
- may not eat pest
- may disrupt food chain
Suggest advantages of artificial fertilisers over natural
- select exact minerals and optimal concentrations
- inorganic ions so more soluble in water so higher rate of uptake of minerals (but eutrophication)
Saprobiotic Nutrition
- extracellular digestion
- secrete enzymes which digest waste and decaying organic matter
Nitrogen Fixation
- free-living nitrogen-fixing bacteria convert atmospheric nitrogen to ammonium
- mutualistic nitrogen fixing bacteria in root nodules of legume plants convert atmospheric nitrogen to nitrates
Nitrification
- two state oxidation
- NH4+ (ammonium) to NO2- (nitrites) by nitrifying bacteria
- NO2- (nitrites) to NO3- (nitrates) by nitrobacter (nitrifying bacteria)
Ammonification
- decomposer bacteria convert nitrogen rich waste products into ammonium
- waste = urea + ammonia
- dead matter = amino acids, DNA, RNA
Denitrification
- denitrifying bacteria convert nitrates to atmospheric nitrogen
Suggest why farmers must plough soil regularly to ensure maximum uptake of nitrates from soil
- denitrifying bacteria thrive in anaerobic, water-logged conditions
- denitrifying bacteria remove nitrates from soil
- ploughing aerates soil
